Shift issues

I have an 88 XJ 4.0 automatic 4wd. I had been having idling issues (which I originally attributed to the IACV that gets replaced every three months) it would idle high on start up and stay there until i cycle it on and off multiple times. The other day I was leaving work and I put it in Drive but it had extremely low power. Checked the trans fluid and it was a little low so I topped it off but still had the problem. I found out I could put it in 1-2 and take off and then shift it manually from 1-2, 3 and then D or 4. Coincidentally the idle issue has gone away. I checked the fuse for the TCM and its still good but replaced it anyways and made sure I had power going to the TCM. Further research led me to the TPS. I replaced it and test drove it but still had the same issue. Not sure where else to go from here. I know the trans is mechanically good since I can shift into all the gears manually so it must be an electrical issue. Any ideas on whats next?

Well just an update in case anybody else runs into the same issue it was my transmission control module. Got out of a junkyard plugged it in and it started working.

Thanks for the update. Sometimes it is as simple as a corroded fuse at the tCU.